During my trip to Milan a couple of weeks ago I was able to attend the main Sunday Mass in the Cathedral, for the Sunday after Ascension Day. It was presided over by the Cardinal Archbishop (one of last year’s papabili) and was liturgically spectacular (particularly when the Easter candle was slowly winched all the way to the roof) but the music didn’t really match up. A largish choir of men and boys sang a largely unison mass setting and a couple of hymns (one of which, disconcertingly, went to the tune of Hark! the herald angels sing). No music was supplied to the congregation.
Last autumn in Venice I fared rather better. At the main Sunday Mass in San Marco a mixed-voice choir sang a 19th century (or pastiche of the style) four-part setting, though not a very interesting one. I also went to a Mass for All Saints’ Day there; no choir, but a sheet with the words and music to several hymns so that the congregation could join in.
The best I’ve done in an Italian cathedral was a mass in the Duomo in Florence, I think the last Mass of Sunday morning. The music came from a small book of plainchant melodies which we were given.